1. Field of the Invention
The present invention relates to an image pickup apparatus, such as a single-lens reflex (SLR) camera, equipped with a focal point adjusting unit.
2. Description of the Related Art
Hitherto, a control method has been widely known which drives an imaging lens simultaneously with the movement of a subject in order to keep the moving subject in focus for a camera having a focal point adjusting unit.
A photographer performs the focal point adjustment by capturing (including) a subject in a focal-point detection area arranged on a photographing screen (viewed on a viewfinder). Focal point adjustment is beneficial in keeping the subject focused when photographing a moving subject, by implementing panning photography. As generally understood by persons of ordinary skill in the art, panning refers to the rotation in a predetermined plane of a still or video camera to track in time a moving subject. In still photography, panning is used to suggest fast motion. That is, photographic pictures are usually noted by a foreground subject in action appearing still (e.g., a runner frozen in mid-stride) while the background is streaked and/or skewed in the apparently opposite direction of the subject's travel. In video display technology, panning refers to the horizontal scrolling of an image that is wider than the display.
However, when a photographer implements panning photography, capturing a subject into the focal-point detection area is not easy. A condition that the photographer may not track the subject may often occur. Under the condition, when a focal point detecting operation and a focal point adjusting operation are performed, the main subject actually desired to be photographed may not come into focus while an object that is not the main subject may come into focus.
Previous attempts to solve the above problem have been proposed. Japanese Patent Application Laid-Open No. 09-105970 discloses means for using a shake detecting unit which detects a camera shake and, if the camera shake may not be fully corrected even by shake correcting means having a displaceable optical element provided in an optical system, preventing a focal point adjusting operation.
Japanese Patent Application Laid-Open No. 11-326743 discloses means for using a shake detecting unit which detects a shake of a camera to detect a shake at a speed or acceleration of a predetermined value or higher, determining that there is a high possibility that the photographer may not track a subject if detected, and preventing a focal point adjusting operation.
However, according to the prior arts disclosed in Japanese Patent Application Laid-Open Nos. 09-105970 and 11-326743, when a photographer is panning with excessively sharp movements or for prolonged periods of time, a subject may not be kept within the focal point detection area. More specifically, even when a photographer securely captures a main subject in a focal-point detection area, the focal point adjusting operation using a detection result by the focal point detecting unit is not performed if the amount of shake of a camera is equal to or higher than a predetermined value. As a result, an image may be obtained in which the main subject is not in focus.